1. Field of the Invention
This invention relates to a hand operated device for bending metal bars, such as bars used to reinforce concrete, generally known as rebars, and in particular to such a device which is portable, can be used on the ground at construction sites and which is capable of bending and straightening rebar.
2. Description of Prior Art
U.S. Pat. No. 4,594,875, issued June 17, 1986 to the inventor hereof, discloses and claims an improved rebar bending machine which is lightweight, hand operated and adapted to be used in the field by a single person. It has a laterally stabilized, elongated base and, mounted to the base, a pair of spaced apart forming posts which straddle a slide mounted pair of lugs that form between them a groove into which rebar to be bent is placed. The slide is movable in an elongated guideway in a direction perpendicular to a line interconnecting the centers of the forming posts so that the groove defined by the lugs can be moved from a first position, at which a rebar placed in the groove is substantially tangent to the peripheries of the posts, past the line interconnecting the post centers, to a second position on the other side of the posts. In the course of this linear movement of the grooves a bend is formed in that portion of the rebar disposed between the lugs, Depending upon the length of travel of the lugs a bend of less than, equal to or greater than 90.degree. is formed in the rebar although 90.degree. bends are by far the most common.
That patent further discloses to generate the relatively large bending forces with an elongated handle that is pivotally attached to the base on the side of the posts which is opposite the side in which the rebar holding groove is substantially tangent to the post peripheries. Suitable linkage connected to the handle and the slide translates the pivotal handle movements into linear slide motions.
To minimize the weight of the bending machine, and to maximize the bending force, the slide, post and linkage are arranged so that the slide does not travel substantially more than the distance it must travel to effect the greatest bend in the bar, typically a bend of not more than about 120.degree.. In this manner, the overall length of the device in general and of the slide, base and guideway in particular can be minimized, which saves weight, labor and costs. Within a given size and configuration of the machine, the bending force that can be generated with the manually operated handle can be maximized. An effective, high speed and accurate bending of the rebar is thus possible with the device of that patent.
Bending machines constructed in accordance with the above-mentioned patent have been on sale for more than a year and have met with exceptional success, It is believed that the success is to a large extent attributable to its compact size, relatively low weight and to its easy operation even on the uneven ground frequently encountered at construction sites.
At construction sites it is sometimes necessary to straighten previously bent rebar. This may be to undo a previously erroneously formed bend, to a need to reform a previously bent bar for use in a different application, or the like. Since the straightening of previously bent bar requires the same force as is required to form the original bend, a machine is necessary to accomplish it. The bending machine disclosed in the above discussed patent is not well suited to perform this task (unless the bend is only slight and substantially less than 90.degree.) because a 90.degree. bent rebar, for example, in the groove between the lugs cannot be simultaneously engaged with the forming posts so that the slide can be operated to straighten the bent section. To accomplish this the travel length of the slide-recounted lugs must be substantially increased. This, however, significantly increases the length of the device, and therewith its weight and cost, which is undesirable.